The Rodgers and Hammerstein musical Oklahoma! debuted on Broadway 71 years ago, and has remained a popular classic ever since. It was a huge hit in its original Broadway run, spawned an Oscar-winning movie version in 1955, and has been performed countless times in theaters worldwide.
In addition to being crowd-pleasing, though, it was also a ground-breaking production, an important work in the development of the 'book musical,' in which the songs and musical numbers progress the story. That's more or less taken for granted in the modern musical, but it wasn't often the case before Oklahoma! took the stage.